Lifters same size?...yep...PR's...need to check geometry first, to determine the PR length it needs. Mock it up, buy or make your own adjustable PR, do a Valvetrain Geometry check, and order the correct length PR's based on the results. My 2¢.

Stock length pushrods should work with the GT40's, but i would still check them, its good practice. I always make it a point to check the proper pushrod length, even if i think it 'should' work fine. Improper pushrod length puts a ton of stress on the valvetrain, thats already stressed enough. Id definatly check it, dont half *** it. if you break a pushrod or a rocker because of it, you'll wish you had. Just my 2 cents.